Audio plays a significant role in providing a content-rich multimedia experience in consumer electronics. The scalability and mobility of consumer electronic devices along with the growth of wireless connectivity provides users with instant access to content. Various audio reproduction systems can be used for playback over headphones or loudspeakers. In some examples, audio program content can include more than a stereo pair of audio signals, such as including surround sound or other multiple-channel configurations.
A conventional audio reproduction system can receive digital or analog audio source signal information from various audio or audio/video sources, such as a CD player, a TV tuner, a handheld media player, or the like. The audio reproduction system can include a home theater receiver or an automotive audio system dedicated to the selection, processing, and routing of broadcast audio and/or video signals. Audio output signals can be processed and output for playback over a speaker system. Such output signals can be two-channel signals sent to headphones or a pair of frontal loudspeakers, or multi-channel signals for surround sound playback. For surround sound playback, the audio reproduction system may include a multichannel decoder.
The audio reproduction system can further include processing equipment such as analog-to-digital converters for connecting analog audio sources, or digital audio input interfaces. The audio reproduction system may include a digital signal processor for processing audio signals, as well as digital-to-analog converters and signal amplifiers for converting the processed output signals to electrical signals sent to the transducers. The loudspeakers can be arranged in a variety of configurations as determined by various applications. Loudspeakers, for example, can be stand-alone units or can be incorporated in a device, such as in the case of consumer electronics such as a television set, laptop computer, hand held stereo, or the like. Due to technical and physical constraints, audio playback can be compromised or limited in such devices. Such limitations can be particularly evident in electronic devices having physical constraints where speakers are narrowly spaced apart, such as in laptops and other compact mobile devices. To address such audio constraints, various audio processing methods are used for reproducing two-channel or multi-channel audio signals over a pair of headphones or a pair of loudspeakers. Such methods include compelling spatial enhancement effects to improve the listener's experience.
Various techniques have been proposed for implementing audio signal processing based on Head-Related Transfer Function (HRTF) filtering, such as for three-dimensional audio reproduction using headphones or loudspeakers. In some examples, the techniques are used for reproducing virtual loudspeakers, such as can be localized in a horizontal plane with respect to a listener, or located at an elevated position with respect to the listener. To reduce horizontal localization artifacts for listener positions away from a “sweet spot” in a loudspeaker-based system, various filters can be applied to restrict the effect to lower frequencies.
Audio signal processing can be performed at least in part using an audio virtualizer. An audio virtualizer can include a system, or portion of a system, that provides a listener with a three-dimensional (3D) audio listening experience using at least two loudspeakers. However, such a virtualized 3D audio listening experience can be limited to a relatively small area or specific region in a playback environment, commonly referred to as a sweet spot, where the 3D effect is most impactful on the listener. In other words, 3D audio virtualization over loudspeakers is generally most compelling for a listener located at the sweet spot. When the listener is outside of the sweet spot, the listener experiences inaccurate localization of sound sources and unnatural coloration of the audio signal. Thus the 3D audio listening experience is compromised or degraded for a listener outside of the sweet spot.